The present invention relates to a variable cam phaser for an internal combustion engine.
JP 3-53447 B2 discloses a variable cam phaser for the angular adjustment of a camshaft with respect to a drive wheel. By means of this variable cam phaser, the angular adjustment is effected by an annular piston. The annular piston has inner and outer splines of varying lead. The annular piston is slidably mounted in a hydraulic cylinder and defines in the hydraulic cylinder a fluid chamber. The piston is biased by a return spring. The annular piston is axially movable. This movement of the annular piston in the cylinder causes the drive and driven members to undergo relative angular displacement in a direction corresponding to the direction of movement of the annular piston. The cam phaser further includes valve means for pressurizing the fluid chamber for displacing the annular piston in one direction against the return spring or depressurizing said fluid chamber for allowing said return spring to displace the annular piston in the opposite direction and thereby controlling the relative angular position of the drive and driven members. The annular piston is subject to the bias of the return spring via a control sleeve so that the control sleeve follows the axial movement of the annular piston. The control sleeve has an axial bore which constitutes an inlet or an outlet always open to the fluid chamber. The control sleeve has an inner peripheral wall formed with an inner circumferential groove communicating with the axial bore. The inner peripheral wall of the control sleeve defines a space communicating with a drainage. The driven member has an inner circumferential transfer groove and bores connecting the transfer groove to a source of fluid pressure. The transfer groove is wide enough to maintain fluid flow communication with a radial bore extending through the control sleeve during axial movement of the annular piston. This radial bore terminates in a port, namely, a supply port, with which the inner peripheral wall of the control sleeve is formed. The valve means includes a spool slidably mounted in the control sleeve. The spool has a circumferential groove adjacent a land. The circumferential groove of the spool is kept in communication with the supply port to receive fluid pressure, while the land covers the inner circumferential groove of the control sleeve. Shifting the spool in one direction causes the land to uncovers the inner circumferential groove of the control sleeve to communicate with the supply port of the control sleeve via the circumferential groove of the spool, pressurizing the fluid chamber and thereby displacing the annular piston and the control sleeve against the return spring. This displacement continues until the inner circumferential groove of the control sleeve is covered by the land of the spool again. Subsequently, shifting the spool in the opposite direction causes the land to uncover the inner circumferential groove to communicate with the drain space, depressurizing the fluid chamber and thereby allowing the return spring to displace the annular piston and the control sleeve in the opposute direction until the inner circumferential groove of the control sleeve is covered again. In this manner the annular piston can take any position corresponding to a position taken by the spool.
An object of the present invention is to provide an alternative to the variable cam phaser of the above kind.